💚 Fix CORS error when building PDF

No longer load Mathjax JS from Unpkg but Cloudflare.
This fixes #97 and loads a minified JS which is lightweight.

mkdocs.yml

@@ -94,7 +94,7 @@ extra_css:
 extra_javascript:
   - assets/javascripts/mathjax.js
   - assets/javascripts/mkdocs-exporter.js
-  - https://unpkg.com/mathjax@3/es5/tex-mml-chtml.js
+  - https://cdnjs.cloudflare.com/ajax/libs/mathjax/3.2.2/es5/tex-mml-chtml.min.js
   - https://cdnjs.cloudflare.com/ajax/libs/mermaid/10.9.1/mermaid.min.js
 
 # Customizations